The present invention relates to a method of producing a round-shape wafer on which a laser mark for indication of a crystal orientation is put instead of a notch or orientation flat.
A wafer sliced off an ingot is processed in various steps such as lapping, chamfering and etching. A mark for indication of a crystal orientation is carved on an edge of the wafer used in these steps. The mark is used for setting the wafer, when the wafer is scribed along a cleavage plane for instance.
Such marks are put on wafers by various methods.
OF method is the most popular one by which an orientation flat is formed at an edge of a wafer. The orientation flat is used for specifying a crystal orientation of the wafer in the subsequent processing steps. However, it is difficult to precisely align a wafer using the orientation, since the orientation flat is formed in a relatively broad area crossing an edge of the wafer at an obtuse angle. Besides, the orientation flat puts restrictions on a shape of an electrostatic chuck used for handling the wafer and causes harmful effects on dynamic balance during spin rotation of the wafer.
A notch engraved on an edge of a wafer is also used as a mark for indication of a crystal orientation. In this case, a notched edge shall be polished to specular glossiness, so as to distinctly detect the notched part during measuring in the subsequent steps. Engravement of the notch likely causes induction of residual stresses at the notched part. Although residual stresses put harmful influences on properties of the wafer, it is difficult to completely remove residual stresses.
Notchless wafers having laser marks for indication of a crystal orientation have been recently used in order to avoid these problems. The laser mark is carved on a front or back side of a wafer by partially melting a surface layer of the wafer with irradiation of a laser beam.
In a conventional laser marking method, each wafer is tested by an X-ray analyzer to detect a crystal orientation of the wafer, and a mark for indication of crystal orientation is put on at a proper position. A commonly used crystal orientation is &lt;110&gt;.+-.1 degree. This method requires a marking operation for each wafer, resulting in poor productivity and heavy duty on the X-ray analyzer.